1) Field of the Invention
The present invention relates to pipe couplings for connecting together pipes in a fluid-tight manner.
2) Description of Related Art
In our earlier patent specification GB-A-2249366 we describe a pipe coupling for connecting together the ends of two plain-ended pipes in a fluid-tight manner, comprising a tubular steel casing, a tubular rubber sealing sleeve and tensioning means in the form of screw bolts for tightening the casing around the sealing sleeve. The casing has circumferential flanges projecting inwardly from its axial end. Gripping devices in the form of incomplete frustoconical rings of steel sheet are located within the casing at opposite ends of the casing. The outer edges of the gripping rings engage in the angle between the axial wall of the casing and the flanges. The inner edges of the gripping rings are formed with teeth. When the coupling is placed around the ends of two pipes to be connected and the tensioning bolts are tightened, the casing is tightened around the sealing sleeve and the gripping rings, pressing the sealing sleeve against the outer surfaces of the pipe end to form fluid-tight seals and forcing the teeth on the gripping rings to bite into the surface of the pipes to grip the pipe.
The casing is made from a strip of rolled steel formed into a tubular shape with a longitudinal gap between the free ends of the strip. The free ends of the strip are folded back on themselves and welded to form loops along opposite edges of the longitudinal gap. Pins are inserted into the loops. The tensioning bolts pass through transverse holes in one of the pins and engage in tapped transverse holes in the other of the pins so as to interconnect the two free ends of the casing. Slots are cut in the loops in the region of the transverse holes to provide clearance for the bolts to pass through. When the screw bolts are turned, the transverse pins are drawn towards each other, thus tightening the casing around the pipe ends.
The coupling of GB-A-2249366 has been successful in many fields of applications. It has been found, however, that there can be problems in manufacturing such a pipe coupling for use with pipes of small sizes, say less than 38 mm in diameter. The tensioning arrangement is too bulky for pipe couplings of this size and the coupling is impractical in many small pipe applications on account of the size of the coupling in relation to the space available in the application, the weight of the coupling, and, especially, the cost of the coupling.
There is a need for a coupling having a tensioning arrangement of a size which is reasonable in proportion to the dimensions of the pipe. The design of the coupling should be such that it can be made lighter than the existing coupling and without pins or welded ends which would make the coupling prohibitively expensive to manufacture for most applications. At the same time, the coupling must meet all the performance requirements of resisting internal pressure in the pipeline (typically up to 100 bar), withstanding vibration, withstanding axial loads, and withstanding shock without leaking, as well as being adjustable to accommodate variations in the diameters of the pipes to be joined within manufacturing tolerances. The coupling should not deform under pressure. The coupling should be capable of repeated installation and dismantling without deformation and deterioration in performance.
The specification DE-A-3445807 proposes a coupling using a single screw bolt and nut which pass through and interconnect, flanges on a tubular casing to tighten the casing. When subjected to tightening, and hydrostatic and axial loads of the kind which would be required for the applications contemplated by the present invention, the casing will deform.